linux-kernel - Re: [PATCH v2 2/8] dma-buf/dma-fence: Add dma_fence_check_and

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Message-ID: <07cd6a0c-9975-48ef-bb2e-5e53a042888e@amd.com>
Date: Mon, 1 Dec 2025 17:08:10 +0100
From: Christian König <christian.koenig@....com>
To: phasta@...nel.org, Sumit Semwal <sumit.semwal@...aro.org>,
 Gustavo Padovan <gustavo@...ovan.org>,
 Felix Kuehling <Felix.Kuehling@....com>,
 Alex Deucher <alexander.deucher@....com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin
 <tursulin@...ulin.net>, Huang Rui <ray.huang@....com>,
 Matthew Auld <matthew.auld@...el.com>,
 Matthew Brost <matthew.brost@...el.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 Thomas Hellström <thomas.hellstrom@...ux.intel.com>
Cc: linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
 intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org
Subject: Re: [PATCH v2 2/8] dma-buf/dma-fence: Add
 dma_fence_check_and_signal()

On 12/1/25 16:53, Philipp Stanner wrote:
> On Mon, 2025-12-01 at 16:20 +0100, Christian König wrote:
>> On 12/1/25 14:55, Philipp Stanner wrote:
>>> On Mon, 2025-12-01 at 14:23 +0100, Christian König wrote:
>>>> On 12/1/25 11:50, Philipp Stanner wrote:
>>>>> The overwhelming majority of users of dma_fence signaling functions
>>>>> don't care about whether the fence had already been signaled by someone
>>>>>
>>>
> 
> […]
> 
>>>>
>>>>> +{
>>>>> +	unsigned long flags;
>>>>> +	bool ret;
>>>>> +
>>>>> +	spin_lock_irqsave(fence->lock, flags);
>>>>> +	ret = dma_fence_check_and_signal_locked(fence);
>>>>> +	spin_unlock_irqrestore(fence->lock, flags);
>>>>
>>>> Could this use guard(fence->lock, flags) ?
>>>
>>> guard? You mean a lockdep guard? Do you have a pointer to someplace in
>>> dma_fence who does what you mean / want?
>>
>> E.g. like guard(spinlock_irqsave)(&fence->lock);
> 
> 
> Hmm, but why?
> It's obvious to all readers that I do spin_unlock_irqrestore() here.
> It's very simple code, lock, 1 line, unlock. What would the guard
> improve?

Well you can save using the local variables.

So this:

	unsigned long flags;
	bool ret;

	spin_lock_irqsave(fence->lock, flags);
	ret = dma_fence_check_and_signal_locked(fence);
	spin_unlock_irqrestore(fence->lock, flags);

	return ret;

Becomes just:

	guard(spinlock_irqsave)(&fence->lock);
	return dma_fence_check_and_signal_locked(fence);

Regards,
Christian.

> 
> 
> P.